Fix setting OnlineModelConfig in Java API (#2147)

Author: csukuangfj

sherpa-onnx/java-api/src/com/k2fsa/sherpa/onnx/OnlineModelConfig.java

@@ -140,12 +140,14 @@ public Builder setModelType(String modelType) {
             return this;
         }
 
-        public void setModelingUnit(String modelingUnit) {
+        public Builder setModelingUnit(String modelingUnit) {
             this.modelingUnit = modelingUnit;
+            return this;
         }
 
-        public void setBpeVocab(String bpeVocab) {
+        public Builder setBpeVocab(String bpeVocab) {
             this.bpeVocab = bpeVocab;
+            return this;
         }
     }
 }